Definition of renal function in normal pregnancy is required for the eventual comprehension of changes occurring during toxemia. The proposed research is an extensive investigation of renal function in gravid rats with special emphasis on sudium metabolism. Results will provide a data base for future protocols designed to investigate similar parameters in animals with experimentally produced diseases of pregnancy. Age-matched paired gravid and virgin littermates will be studied. A. Renal function: Glomerular filtration rate (C inulin), effective renal plasma flow (C PAH) tubular secretory(PAH) and reabsorptive (glucose) maxima and parameters of urinary concentration and dilution will be measured in unanesthetized rats. B. Sodium metabolism: 1) Renal response to graded saline infusions will be studied. Infusate volume will be calculated to expand the animals by a volume equal to 5-20% of the virgin littermates' extracellular space. 2) Microsomal Na -K stimulated (ATPase) will be measured in kidneys of saline infused and noninfused paired littermates. Results will be correlated with met sodium tubular transport and evaluated in relation to pretest sodium (and nitrogen) balance. Specificity of the relationship between Na-K-ATPase and sodium transport will be tested by simultaneously evaluating the effect of the latter on other microsomal or membrane-bound enzymes(Mg ion ATPase, glucose-6-phosphatase and 5'nucleotidase) not involved in sodium transport. C. Hormonal milieu of pregnancy: Similar experiments to those described above will be performed on littermate rats given injection of estradiol benzoate, progesterone, and other humeral agents whose secretion is altered during pregnancy. Long term goal of the project is apply information obtained in this study to the understanding of normal and disordered renal function in human pregnancy.